In one conventional sprocket type tensioner lever device, as shown in FIG. 3, a tensioner sprocket is pressed against and meshed with a transmission chain rotatably mounted on a tensioner lever which cooperates with a transmission chain C stretched endlessly between a driving sprocket D and a driven sprocket F. In the tensioner, a lever L disposed alongside the slack run of the transmission chain has a pivoted proximal end LA supported oscillatably around a fixed shaft A and a pivoted free end LB pressed and urged toward a free span section of the slack run of the transmission chain C by a pressing and urging lever R of a tensioner T. A tensioner sprocket S rotatably mounted on the tensioner lever L is meshed with and pressed against the free span section of the slack run of the transmission chain C to properly hold a tension.
Another tensioner lever device is shown in FIG. 4. In this figure, a lever L' has a pivoted proximal end L'A which supports the tensioner lever L' oscillatably around a fixed shaft A, and an oscillating free end L'B is pressed and urged against a free span section of the slack run of a transmission chain C by a pressing and urging lever R of a tensioner T.
It is noted that a travel guide member G for the transmission chain is provided on the tension run of the transmission chain in each of the devices L and L'.
In the above-described prior art, in case of the sprocket type tensioner lever shown in FIG. 3, if the section of the slack run of the transmission chain (hereinafter called the free span section) between the driving sprocket and the driven sprocket is long, a flapping vibration of the chain tends to occur in the free span section, and noises caused by the vibration unavoidably occur. Further, in case of the sliding type tensioner lever shown in FIG. 4, the maximum face pressure is applied to the pressing and sliding surface L'F of the oscillating free end L'B in sliding contact with the bent portion having the minimum radius of curvature formed in the free span section of the slack run of the transmission chain C caused by the pressing action of the tensioner lever L' to increase a sliding frictional resistance, thus increasing a loss of the driving force and a wear loss of the sliding surface L'F.